ECG device with impulse and channel switching ADC noise filter and error corrector for derived leads

Abstract

The present invention provides a device and method for filtering impulsive noise and channel switching noise at ADC in an ECG device with multiplexed ESCs. The filtering is based on an implementation of Burst Sampling technique also a method for correcting errors in derived leads caused by time delays due to sequential sampling of different ECG signals is also provided. Real time digital FIR filters are used for removing other types of noise in ECG signals. The ECG device is compact and light weight and includes features of self calibration, clip detection and drawing of power from USB port of a PC, batteries or an external power source. The ECG monitoring device of the present invention measures real time ECG signals with automated data recording, data storage and retrieval, data transmission / transfer to an external system, along with parameter extraction for ECG analysis in an efficient manner for quick and reliable ECG measurement, in an extremely cost effective manner.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a National Stage filing under 35 U.S.C. §371 of PCT Application No. PCT / IN2010 / 000134, filed Mar. 9, 2010. This application also claims the benefit of Indian Patent Application No. 445 / DEL / 2009, filed Sep. 3, 2009. The entirety of both applications is incorporated hereby reference.BACKGROUND OF THE INVENTION[0002]The present invention relates to a ECG (Electrocardiograph) device with Impulse and Channel Switching ADC Noise filter and an Error corrector for Derived Leads. The present invention more particularly relates to implementation of a Burst Sampling technique for removing Impulsive and Channel Switching ADC Noise from the ECG signal and an interpolation algorithm for correction of errors in Derived ECG Leads caused by sequential sampling of directly measured ECG leads. This invention in particular relates to a medical device for measuring, filtering, monitoring and recording ECG signals. It also relates to extrac...

AI Technical Summary

Benefits of technology

The present invention provides a compact and portable ECG monitoring device that uses a burst sampling technique for filtering out impulsive and channel switching ADC noise, and an error corrector for derived leads caused by time delays. The device is powered by a firmware and can be upgraded easily without changing the hardware. It also provides a high order FIR filter to remove noise outside the ECG pass band. The device includes an isolation buffer, a multiplexer, a signal conditioning and amplifier unit, an averaging circuit, a calibration unit, an ADC, a control unit, a power and data indicator, a communication channel, and a memory unit. The invention allows for standard ECG measurements and flexibility in upgrading and calibration.

Problems solved by technology

On the other hand, the infrastructure and medical instrumentation available is inadequate to cater to the needs of large populations in developing countries.

The capacity of the general masses to pay for medical tests and diagnosis is also very limited.

Moreover, whenever the symptoms of a heart disorder are felt by patients, they have to be rushed to the nearest hospital or medical practitioner, where the ECG of the patient needs to be recorded, resulting in a delay between the time of the occurrence of the event and the ECG recording.

Many available compact palmtop ECG machines with a single ECG channel display only one Lead at a time and thus have low throughput.

Several such low cost machines are further limited to measuring only one ECG-lead and thus provide limited information for medical diagnosis.

This makes the device bulky and comparatively more expensive.

The power consumption of the device also increases.

Another shortcoming of the scheme is that any drift over time in calibration of individual ESC will cause errors for the derived leads.

For derived leads, all the directly measured ECG leads must be sampled at exactly the same instant of time, because the linear combinations of two components of a vector measured at slightly different instants of time will introduce an error in the derived leads.

(a) the ECG voltage signals from different ESCs are multiplexed, and hence not sampled at exactly the same instant of time. As some of the leads are derived from other leads, linear combinations of two components of a vector measured at slightly different instants of time introduce an error in the derived leads and

(b) when each ECG voltage signal is switched and sampled by ADC for digitization, there is always a possibility of a spike / glitch / impulse giving an erroneous reading. Spikes contain frequency components, some of which lie within range of frequencies of the ECG pass band and can not be removed by usual FIR filters. Impulsive noise is noise of short duration, particularly of high intensity, such as that produced by turning on / off of a high mains current device in the vicinity, power fluctuations etc. Moreover, charge injection by the switching of the analog multiplexer can also impose glitches on the S / H output. Channel switching, with the associated sudden voltage change in analog circuits, may also introduce effects like overshoot, undershoot and ringing etc., which may lead to further deterioration of the sampled signal. Both the schemes used in Model 1 and Model 2 of Shared ADC setup use multiplexing and switching of signals which may introduce “Channel Switching Noise”.

But such assumption is not always true, because real-life muscle noise has sometimes impulsive character.

These filters are non-linear and computationally inconvenient.

Also, the reduction obtained in muscle noise is at the cost of distortion in the ECG signal of interest.

Many filter implementations are of the IIR type which in principle can be unstable.

The filtering methods used in above prior art depends on IIR filter which in principle can become unstable.

A study of the prior art reveals that the existing ECG monitoring devices do not address the removal of Channel Switching ADC Noise and glitches / spikes.

The classes of multiplexed ECG signal measurement devices also do not address any method for correcting the digitized ECG signal points for time delay in switching between different channels.

Some of them use IIR filters which are not necessarily linear and, in principle, can be unstable.

Some of the devices simply monitor and display ECG signals and thus provide no ECG data recording capability at all.

Others record ECG data and provide only for the local playback of recorded data and thus provide no remote diagnostic capability.

Still other devices use bulky and expensive hardware circuitry for calibrating the device, filtering the signal using analog low pass and high pass filters etc and for clip detection.

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